Lacustrine Deposits

20 million years ago, before the Sea of Japan was formed, the land of the Oki Islands is thought to have been at the bottom of a huge lake. In the coastal areas of Dōgo Island, we can see sandstone and conglomerate rock that were deposited in lakes and rivers on the edge of the continent. Since they contain fossils of temperate climate plants such as the jolcham oak (Quercus serrata), as well as river snails (Family Viviparidae) and other freshwater shellfish, they tell us about the environment of Oki before the Sea of Japan was formed.